Process for the production of bisulphite solutions



Feb. 14, 1939.

G. HAGLUND PROCESS FOR THE PRODUCTION OF BISULPHITE SOLUTIONS OriginalFiled F'eb. 24. 1937 Gus-WF HHGLUND Se* @y FITTORN EY Patented Feb. 14,1939 PROCESS FOR THE, PRODUCTION OF BISUL- PHITEr SOLUTIONS GustafHaglund, Storangen at Stockholm, Sweden Original application February24, 1937, Serial N o. 127,379. Divided and this application September21, 1937, Serial No. 164,861. In Germany March 3, 1936` 3 Claims.

This invention relates to the production of bisulphite solutions, andmore particularly to a process for the production of calcium bisulphitesolutions of the kind used in the production of 5 sulphite cellulose orpulp. The object of the invention is to provide an improved process forthe production of such solutions from a lime-bearing material in lumpform. The present application is divided out from applicants coi-pendingapplication Serial No. 127,329, led February 24, 1937, in which asuitable apparatus for carrying out such a process is claimed.

In present practice the processes for the production of calciumbisulphite liquor (raw acid) where limestone in lump form is used aregenerally carried out in a plant consisting of twotowers lled with thelimestone and connected with each other to form a system wherein sulphurdioxide gas is passed upwards through the towers in seriescounter-current to water supplied to the system and the acid formed inthe towers. In the reactions taking place on the formation of the acidthe limestone is consumed in a different degree in the two towers. Thestrongest consumption of limestone takes place in the tower where thefresh S02 gas is introduced into the tower system and where thestrongest acid is obtained (strong acid tower), and in order to obtain auniform consumption of limestone in both towers the order of the towersin the system is changed at intervals. In any case, the weak acid formedin the first tower for the moment serving as weak acid tower istransferred from the bottom of said tower to the top of the strong acidtower and trickled down through the latter from the bottom of which theresulting liquor is then discharged.

The above-mentioned process, however, has several objectionablefeatures. So, for instance,

even under normal working conditions it is practically impossible toproduce continually a raw acid of constant composition especially onaccount of the iniiuence of the temperature on the speed of reaction.Consequently, in winter time the composition of the acid obtained isdifferent from that obtained in summer time. Further, such plants aregenerally built for the production of a certain quantity of raw acid ofa substantially denite composition and a change in the V quantityproduced will also result in a change in the composition of the acid.For the same reason, a regulation oi the composition of the acid cannotbe effected while maintaining the quantity unaltered. Generallyspeaking,there is little or no possibility of compensating in another direction achange occurring in one respect, nor, consequently, of regulating theworking in said process.

It is further also proposed, in connection with such a two tower system,to use a supplemental limestone tower through which the liquor obtainedfrom said tower system may be circulated. Hereby the content of lime inthe liquor may be increased, when necessary, but also in this case thereis no'possibility of eiecting a satisfactory regulation in dilerentdirections.

'Ihe object of the present invention is lnow to provide a processwhereby it is rendered possible to avoid the above-mentioneddisadvantages and to obviate the difficulties connected with theproduction of sulphite acid liquor when using 1imestone in lump form, sothatindependent of the conditions prevailing-a liquor of predeterminedcomposition can be obtained.

Another object of this invention is to provide such a process by meansof which the manufacture of such sulphite acid liquor can be carried outin a cheap and simple manner and with the use of an apparatus of a cheapand simple construction and of comparatively small dimensions.

A still further object of the invention is to provide measures wherebythe diiculties caused by `the soi-called hanging in the limestone massare removed.

The main and principal feature of the new process according to theinvention consists in the circulation through the lower portion of aconvlined mass of lime-bearing material in lump form `fed downwardly ofthe solution resulting from the action of SO2 gas and water upon saidlimestone, said agents being passed in counter-current relationshipthrough'the lime-stone mass. This circulation is an integrant part ofthe process and by increasing or reducing the quantity and rate ofcirculation in relation to the different working conditions thecomposition of the liquor can always be regulated as desired.

Thus, for instance, if under certain working conditions including thecirculation of a certain quantity of solution per time unit a liquor ofa certain composition is obtained and it is desired to produce a liquorhaving a lower content of lime it is only necessary to reduce thequantity of circulation correspondingly, the other working conditionsbeing kept constant. By suitably regulating the circulation -in relationto the quantity and composition of the SO2 gases as well as the watersupplied the content of lime in the liquor can be adjusted to correspondto a predetermined Value and at the same time a complete absorption ofthe sulphur dioxide may be compassed.

Generally speaking, in the present process a change of any of thefactors having an influence upon the production of the acid may easilybe equalized or compensated by changing the quantity or rate ofcirculation in the lower reaction zone. r

This process can be carried out in a single limestone tower ofcomparatively small dimensions but Y nevertheless great capacity.

In order to ensure a satisfactory distribution of the circulating liquorover the limestone in said lower portion of the limestone mass it ispreferred to cause the descending mass to defiect laterally in such away that the circulated liquor can be spread from above over thelimestones in said lower portion thereof.

Further in a preferred manner of working a higher rate of sinking of thedescending limebearing material is maintained in the upper portion ofthe reaction zone (where the consumption of said material iscomparatively low) than in the lower portion thereof (where thecirculation of the liquor takes place), so as to prevent a hanging ofthe limestone in the first-mentioned portion of the reaction zone.

In such cases where a raw acid of denite, preferably high content oftotally free SO2 is desired, the raw acid produced as described andhaving a definite content of lime is enriched in totally free SO2. Thismay be effected in different ways, for instance, as known per se, bypassing said raw acid through a mass of insoluble interstitial materialin countercurrent flow to sulphur dioxide gases passing therethrough.

In the preferred manner of working according to the invention, however,the resulting liquor is then collected from the bottom of the mass ofinterstitial material and circulated through the lower portion thereofin a way similar to that described above in connection with the mass oflime-bearing material. In this process the extent of circulation may beregulated to ensure a desired, predetermined content of free SO2 in theliquor.

In this manner it is possible to accommodate exactly the composition ofthe acid to different conditions of digestion and to regulate the samewith regard to the quality of the pulp to be produced.

The process according to the invention is described below in greaterdetail in connection with the accompanying drawing which shows one formof apparatus with which said process may be carried out.

In the drawing I designates a limestone tower comprising an uppersection 2 anda lower section 3, and 4 is the filling of limestone inlumps in the tower. At the top the tower has an opening provided with acover or lid 5 for introduction of the limestones into the tower.Further, there is arranged a water supply pipe 6, a water-meter l, avalve 8, a trickling device or sprinkler 9, and a gas exhaust pipe I Il.

The two sections of the tower may be of a cylindrical form. In the formof apparatus shown in the drawing said sections are arrangedconcentrically in relation to each other, and the diameter of the lowersection is considerably greater than that of the upper section. In thelower section there is in the centre built a middle part I I whichserves to deflect laterally the limestone lling sinking downwards fromthe upper section of the tower on its passage into the lower section andto spread out and distribute it in such away that there will be a freespace between the limestone lling and the upper wall of the lowersection of the tower. The limestone filling in the tower is supported bya grating I2 in the tower section 3. In the free space I3 under saidgrating I2 opens the supply pipe for the SO2-gas. The lower part of thisspace I3 serves as a collecting chamber I 5 for the liquid passingthrough the tower or the bisulphite solution (acid) which has beenformed. By means of the pipes I6 and I8 connected by the pump I'I saidchamber is connected with the free space above the limestone filling in4the upper part of the section 3 where trickling devices or sprinklersI'I are arranged in a suflicient number and suitably disposed. The pumpI1 is preferably so dimensioned that it can transfer a quantity ofliquid, which is several times as great as the quantity supplied by thepipe 6. For the discharge of the raw acid formed from the acid chamber I5 there is arranged an overflow pipe 2| with the branch pipe 44.

In case the acid produced in the limestone tower I in conformity withthe above is to be enriched in its content of free SO2, said acid may betransferred through the pipe 2I to a second tower 24 by means of thepump 22 and the pipe 23 which ends in a sprinkler 36. The tower 24 whichgenerally can be considerably smaller than the tower just describedcomprises like the latter an upper section 25 and a lower section 26 ofa greater diameter. In the form of apparatus shown in the drawing thesections 25 and 26 are both provided with a lling 21 of an interstitialmaterial such as rings, coke, pumice stones or the like of an insolublematerial which are supported by gratings 28 and 29 arranged in the lowerpart of said tower sections 25 and 26. A middle part like the part I Iin the tower I is here superfluous. Under the grating 29 there is a freespace serving as a collecting chamber 30 for the acid which has beenproduced. Into said chamber also a gas supply pipe 3| opens whichbranches off from the main gas supply pipe 4I). Said main gas pipe 40 isalso connected with the gas supply pipe I4 leading to the tower Ialready mentioned. The chamber 36 is further by means of the pipes 32and 34 connected, via the pump 33, with the upper part of the towersection 26 where the pipe 34 ends in a trickling device 35 arranged inthe free space above the lling. For the discharge of the acid from thechamber 30 an overflow pipe 39 is arranged and for the gas escaping fromthe upper tower section 25 there is a discharge pipe 31 connected withthe gas supply pipe I4.

With the use of this apparatus the process according to the inventionmay be carried out in the following manner.

If it be supposed that at first only the limestone tower is to be setworking, the valves 4I and 43 in the gas supply pipes and the valve 46in the overflow pipe 2| are kept closed, while the valves42 and 45 arekept open. The SO2 gas is for instance introduced at the bottom of thetower I direct from sulphur or pyrite furnaces through the pipes and I4.At the top of the tower the pipe 6 continually supplies a quantity ofwater regulated in relation to the quantity of acid to be produced andtrickled down through the tower. By means of the circulation pump I1 theliquid collected in the chamber I5 is circulated through the lowersection 3.

By appropriate regulation of the valves 8, 20 and 42 the absorption andreaction conditions may be regulated in such a way that the SO2 contentof the gasesmay be practically wholly absorbed in the tower, and at thesame time a raw acid of definite composition can be obtained. The uppersection of the limestone lling serves here especially for theachievement of a complete absorption of the SO2-content of the dilutedgases passing upwards from the lower tower section which are herebrought into contact with fresh water and limestone. In the lower towersection on the other hand the dissolution of the lime takes placewhereby a solution of the desired lime content is obtained. If namelythe valve 20 is kept more or less open, the supply of water and gasbeing kept constant, the quantity of liquid circulated through the towersection 3 or the rate of circulation and consequently also the quantityof lime dissolved, that is the content of lime in the raw acid, willchange correspondingly, said acid being discharged through the overiowpipe 2l and the branch pipe 44 in a quantity corresponding to the supplyof water.

The absorption of the SO2 and the dissolution of the lime is in this wayperformed in a very eiective manner. Said reactions are namely in a highdegree promoted by the effective sprinkling of the limestone filling andthe circulation in the lower tower section where there is a very bigtotal surface of the limestones, which are continually decreasing insize during their passage downwards. At the same time the circulationprevents the grating from being clogged up. On account of this and alsobecause of the comparatively high sinking rate of the limestone fillingin the upper narrow tower section where the consumption of lime iscomparatively low also the so-called hanging of the limestone filling isprevented.

The eiiiciency of the process described is, consequently, very high andthe tower may, therefore, be comparatively small in size andnevertheless have a great capacity.

If in the acid owing out from the limestone tower the content of totallyfree SO2 is to be increased, said acid is transferred into the tower 24.For this purpose the valve 45 is closed, the valves 4l, 43, 46 and 38are opened and the pumps 22 and 33 started. (For the present it may beassumed that also the valve 42 is closed.)

The raw acid from the limestone tower l is then introduced into andtrickled down from the top of the tower 24. I-Iere it meets the SO2 gassupplied from the pipe 3| and passing upwards through the tower whereits content of SO2 is partly absorbed by the acid trickling down. Thelime content of the acid being constant, the composition of the acid isthus changed only with regard to its content of free SO2. Said contentof free SO2 may be varied as desired with regard to the utilizationpurpose of the acid by appropriate regulation of the quantity of acidcirculated through the lower tower section. Like the pump 22 the pump 33is so dimensioned that it can transfer a quantity of liquid severaltimes as great as that supplied to the top of the tower. The raw acidthus enriched in SO2 is then discharged from the tower through theoverflow pipe 39.

The gas escaping from the top of the tower section 25 which generallystill has a rather great content of SO2 is then through the pipes 3l andI4 transferred to and introduced into the tower l where it is utilizedin the manner described above. In this case, consequently, it is assumedthat the SO2 gas before being supplied to the tower l has been passedthrough the tower 24.

In such cases, however, where the two towers 24 and l are operatedsimultaneously, the SO2 gas may also be supplied to the tower I partlydirect from the pipe 40, partly via the tower 24. In the last-mentionedcases the valve l2 is also kept open and is regulated in the appropriatemanner.

The method'described renders it possible when using limestone in lumpsto produce continually bisulphite solutions of denite compositionaccording to the conditions occurring by means of a very simple andcheap process and without diiiiculties caused by interruption inworking. Further the process may be carried out in a plant which incomparison with the plants of this kind already known and having thesame capacity is considerably smaller in size and, consequently, theplant will also entail considerably lower building costs.

The process according to the invention may also include the productionof magnesium bisulphite solutions or solutions containing magnesiumbisulphite which may be obtained for instance by using dolomite insteadof lime.

It should further be pointed out that in the process described suchalterations and modifications may be undertaken as do not influence thefundamental principle of the same and which lie within the scope of theinvention.

Having now particularly described the nature of my invention and themanner of its operation, what I claim is:

1. A continuous process for the production of bisulphite solutions ofthe kind used in the manufacture of sulphite pulp, which comprisesfeeding downwardly a confined mass of a lime containing material inpieces, causing the descending mass to deflect laterally at a pointsubstantially above its lower extremity, spraying water over the massfrom the top, passing SO2 containing gas upwardly through the mass,thereby causing a reaction between the lime containing material, thewat-er and the sulphur dioxide to form a bisulphite solution, collectingthe resulting solution from the bottom of the mass, continuouslyreturning solution tothe point where the descending mass of limecontaining material is deflected laterally and spraying it from aboveover said laterally defiected lower portion of the mass, andcontinuously discharging the resulting bisulphite solution from thereaction zone.

2. A continuous process for the production of bisulphite solutions ofthe kind used in the manufacture of sulphite pulp, which comprisesfeeding downwardly a confined mass of a lime-bearing material in lumpform, causing the descending mass to deflect laterally at a pointsubstantially above its lower extremity, spraying water over the mass`from the top, passing SO2 containing gas upwardly through the mass,thereby causing a reaction between the lime-bearing material, the waterand the sulphur dioxide to form a bisulphite solution, collecting theresulting solution from the bottom of the mass, continuously returningsolution to the point where the descending mass of lime containingmaterial is deflected laterally and spraying it from above over saidlaterally deected lower portion of the mass, the extent of circulationbeing regulated to ensure a` predetermined base content in the resultingsolution, continuously discharging theliquor from the reaction. zone,and then passing the liquor thus obtained through an absorption tower incountervcurrent relationship to SO2-containing gases to increase thecontent of free S02 in the solution.

3. A continuous process of producing sulphite acid liquor, whichcomprises passing SO2 Containing gases successively through a confinedmass of an insoluble interstitial material and a mass of limestone inpieces, said mass of limestone being fed downwardly Within a conned zoneand .caused to deect laterally at a point substantially above its lowerextremity, spraying Water from above over the mass of limestone, therebycausing the water, the limestone and the sulphur dioxide to react witheach other to form a calcium bisulphite solution, collecting saidbisulphite solution from the bottom of the mass of limestone,continuously circulating the solution through the GUSTAF HAGLUND.

